Discharge element, method of producing the same and apparatus comprising the same

ABSTRACT

A discharge element comprises a linear electrode and a sheet electrode both of which are provided opposite to each other with an insulator sheet therebetween, in which the linear electrode is formed by plasma spray coating a high-meting point semiconductor so as not to be worn when a high-frequency high voltage is applied between both electrodes.

This is a continuation of co-pending application Ser. No. 07/696,713filed on May 7, 1991 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a discharge element used for producingozone from air or oxygen, charging and destaticizing powder, chargingand destaticizing photoconductive insulating films used in electroniccopying machines, treating plastic surfaces and the like. The presentinvention also relates to a discharge apparatus comprising a combinationof the discharge element with a power source for driving the element, adischarge treatment apparatus comprising a combination of the dischargeelement with an auxiliary device, a power source and a handling deviceand the like.

This type of conventional discharge element has a conductive linearelectrode mainly composed of a metal and provided on the surface of aceramic insulator and a sheet electrode provided therein. When ahigh-frequency silent creeping discharge is produced on the surface ofthe ceramic insulator by applying a high-frequency high voltage betweenboth electrodes, the linear electrode becomes worn and irregularlydeformed, or the linear electrode is partially melted, scatters andadheres to the surface of the ceramic insulator. This causes adisturbance in the electric field and a deterioration in the efficiencyof the electrode serving as an ion source. Apart from the melting of theelectrode, this phenomenon is sometimes caused by the oxide produced byoxidation of the surface of the electrode having a low melting point andthe property of easily separating.

In order to solve the above-described problem, the surfaces of thelinear electrode and the ceramic insulator are coated with melted glassglazing, a ceramic thin film or the like. However, a thin coating filmcannot withstand use for a long time and a thick coating film causesdifficulties in generating ions due to the insulating properties betweencoating films and brings about the need for application of a voltagehigher than that applied in a case without any coating film. In the caseof a glazing layer, fine particles are generated from the glazing layerduring discharge because the melting point thereof is not so high. Thusthe treated gas produced when a discharge element is employed fortreating the gas is sometimes contaminated with the fine particles. Thecontamination has a significant effect on the quality of the product towhich the treated gas is applied. Particularly, when ozone is producedfrom boron used as a raw material by using a discharge element providedwith glazing in accordance with the prior art and is used for ashingsemiconductor products, if alumina is used as a ceramic insulator forthe discharge element, the gas containing the produced ozone iscontaminated with oxygen inevitably contained in the glazing material.This sometimes has a significant adverse effect on the quality of asemiconductor product.

In addition, in the prior art, fine ceramic represented by alumina of92% or more purity is used as an insulator and has a conductive linearelectrode integrally formed on the surface thereof and a sheet electrodeintegrally formed therein. A method generally used for thick filmmultilayer printed ceramic substrates is employed for forming bothelectrodes in which both electrodes are printed by a thick filmtechnique on the insulator in the form of a green sheet before burning,pressure-welded and then metallized by burning at a high temperature fora long time in a hydrogen atmosphere. In the discharge element producedby the above method, only paste containing as a main material tungstencan be used as an electrode material because the thermal expansioncoefficient of the alumina ceramic used as the insulator must agree withthat of the electrode material within the wide temperature range fromroom temperature to about 1500° C. However, since tungsten is easilyoxidized at a high temperature, the electrode is worn by the oxygencontained in the atmosphere in which the discharge element is used, andthe efficiency cannot be stably maintained for a long time. In addition,in the above-described method of producing a discharge element, whichmethod is generally used for thick film multilayer printed ceramicsubstrates, although semiconductor ceramic is used as an electrodematerial, since a semiconductor literally has a high electricalresistance the efficiency deteriorates due to the generation of heat inthe electrode which results in a decrease in the applied voltage in aportion of the electrode away from a feeding portion, which is caused bythe voltage drop of the electrode resistance even if only the materialfor the electrode structure is replaced by a semiconductor material. Noelectric field apparatus which can be brought into practical use canthus be obtained.

The above-described methods also have the critical disadvantage that theproduction cost is high because the production equipment is expensive,and the production of a discharge element requires much time.

Apart from the above prior art, the ozonizer electrode shown in FIGS. 20and 21 comprises a rod electrode 42 formed on one surface of adielectric substrate 41 with a spacer 44 for keeping a distance ltherebetween and a sheet dielectric electrode 43 formed on the othersurface, the rod electrode 42 being made of conductive ceramic havingelectric conductivity of 10² Ω⁻¹ cm⁻¹ or more at 20° C., the sheetdielectric electrode 43 being made of conductive ceramic or a metal, andan a.c. high-voltage power source 46 being connected between the rodelectrode 42 and the sheet dielectric electrode 43. In this case,although a boron compound is suitable as a conductive ceramic material,a boron compound has a critical problem with respect to chemicalcontamination of the semiconductor produced when ozone is used fortreating semiconductors, as described above. In addition, if the purityof the conductive ceramic is increased for obtaining high efficiency,the difference between the thermal expansion coefficients of theelectrode and the substrate is increased. This mainly causesdifficulties in fixing the positional relation between the dielectricsubstrate 41 and the rod electrode 42 and a problem with respect to thelong-term stability of the electrode efficiency. Accordingly, it is anobject of the present invention to solve the above problems ofconventional discharge elements. Namely, the object is to improve thedurability of a conductive linear electrode so as to prevent the linearelectrode from being worn, irregularly deformed, by locally scatteringand adhering to the surface of a ceramic insulator when a high-frequencyhigh voltage is applied between both electrodes. The means for improvingthe durability brings about an improvement in the efficiency of thewhole electrode and a reduction in the production cost, withoutdeteriorating the ability to generate ozone.

It is another object of the present invention to curtail the overallcost of an apparatus comprising a discharge element by reducing thenumber of steps required for actually incorporating the dischargeelement into the apparatus. For example, in the ozone generating elementshown in FIGS. 17, 18a, 18b and 19, which is formed by employing theconventional technique of producing multilayer ceramic printedsubstrates, a glaze coating film 24 must be provided for preventing thewearing of the linear electrode 22 formed on a surface of an aluminasubstrate 21 and containing tungsten as a main component. In addition,it is necessary to pass a feeding portion 22a for supplying electricityto the linear electrode 22, through a through hole 27, form a nickellayer for soldering on the surface of the feeding portion 22a, place asolder layer 25 on the nickel layer and solder a feeder 26 to the solderlayer 25. In this case, the feeding portion 22a and the through hole 27do not contribute to the generation of ozone but produce an increase inthe cost caused by unnecessary increases in the sizes of the element andthe container for receiving the element.

In addition, it is necessary for supplying electricity to a metal sheetelectrode 23 containing tungsten as a main component to form a nickellayer 28 for soldering, place a solder layer 25 thereon and soldering afeeder 26 to the solder layer 25. The ozonizer electrode shown in FIGS.20 and 21 also has such complicated structure and assembly and,particularly, they have a significant problem with respect to the needfor a great cost for assembly including soldering. Further, when theelement is sealed in a container having an inlet and an outlet and used,as in a general ozone generating apparatus, there is often the criticalproblem that the solder layer 25 is eroded by the ozone with the passageof time during use, and feeding finally becomes impossible.

It is a further object of the present invention to decrease theproduction cost of a discharge element by simplifying the method ofproducing the discharge element and to widen the applicability of thedischarge element by widening the range of materials for the elementwhich can be used according to the purposes of use.

SUMMARY OF THE INVENTION

The present invention provides a high-efficiency discharge element withhigh durability comprising an insulator sheet (referred to as "ceramicinsulator" hereinafter) made of ceramic, glass, crystallized glass,enamel or the like, a sheet electrode provided on the rear side of theinsulator sheet, and a high-melting point semiconductor linear electrodeformed on the surface opposite to the sheet electrode by flame spraycoating. The present invention also provides a method of producing adischarge element comprising providing a masking member on the surfaceof a ceramic insulator sheet by screen printing so that the maskingmember adheres to the surface, forming at least one of a high-meltingpoint semiconductor linear electrode and a sheet electrode by flamespray coating and then removing the masking member. The presentinvention further provides a silent discharge generating apparatuscomprising the discharge element in which, when an a.c. high voltage isapplied between the sheet electrode and the linear electrode, which areprovided with the ceramic insulator sheet therebetween, uniform silentdischarge is generated around the linear electrode.

In the discharge element of the present invention, when an a.c. highvoltage from an a.c. high voltage source is applied between the sheetelectrode provided on the rear side of the ceramic insulator sheet andthe high-melting point semiconductor linear electrode provided on thesurface opposite to the sheet electrode, an a.c. silent creepingdischarge is generated around the linear electrode centered on thesurface of the ceramic insulator sheet on the linear electrode sidebetween both electrodes. The discharge element is thus used forelectrically charging articles such as powder, films and the like byextracting a large amount of unipolar ions from the discharge region,destaticizing articles by alternately extracting a large amount ofpositive and negative ions, modifying the surfaces of articles andpowder by treating them in the discharge region, or effecting chemicalreaction, e.g., ozonization of oxygen, by employing a gas reaction inthe discharge region.

In these cases of use, since the linear electrode at the center of ahigh frequency silent creeping discharge is subjected to collisions withions and electrons in a strong electrical field, the surface of theelectrode is locally heated to a high temperature, and a difference intemperature thus occurs between the linear electrode and the ceramicinsulator sheet. However, because the ceramic insulator sheet is made ofa material such as alumina or the like which has good thermalconductivity, and because the linear electrode is formed by flame spraycoating a high-melting point conductive ceramic material such as TiN,TaN or the like, which is chemically stable, on the insulator sheet soas to have a width of 1 to 0.25 mm, a thickness of about 0.01 to 1 mm,in a rectangular sectional form and a structure in which the long sideof the sectional form adheres to the ceramic insulator sheet, theelectrode is sufficiently cooled. Further, since the electrode is formedby flame spray coating, the electrode is made of a semiconductor havingporosity of 2.5 to 12.5%. Because the linear electrode thus hasresistance to sudden changes in temperature with position and time, itis not worn. Although the specific resistance value of the high-meltingpoint semiconductor linear electrode is about 10⁻³ to 10⁻¹ Ωcm, thepurposes of use can be satisfactorily achieved by appropriately formingand connecting the electrode, as described below. It is said that, inthe case of a high-frequency creeping discharge electrode as in thepresent invention, sufficient efficiency cannot be obtained unless thespecific resistance is 10⁻³ Ωcm or less. This applies to the case of arod electrode sintered together with additives. In this case, theprocess of sintering the rod electrode requires much time for operatingthe sintering apparatus used, thereby increasing the cost, and the rodelectrode is insufficiently cooled due to the poor adhesion of the rodelectrode to a dielectric substrate. This causes an increase in thetemperature of the electrode and acceleration of decomposition by ozone,as well as the problem that a difference in thermal expansion betweenboth materials causes difficulties in fixing the relative positionbetween the dielectric substrate and the rod electrode and in feeding.As described above, the present invention is capable of solving theabove problem.

In the discharge element of the present invention, the linear electrodecan be formed on the ceramic insulator sheet so as to adhere thereto byonly a simple process such as flame spray coating for a short time. Thedischarge element thus has many advantages to practical use that manyelements can be produced at low cost, and that the sizes of the elementand an apparatus comprising the element and the production cost can bereduced because there is no need for soldering for feeding and mountingand the processing related to the soldering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an ozone generating apparatus comprising adischarge element of the present invention which is also a plan view ofa portion including the line I--I in FIG. 2;

FIG. 2 is a sectional view taken along the line II--II in FIG. 1;

FIG. 3 is a plan view of the discharge element as a component of theapparatus shown in FIG. 1;

FIG. 4a is a sectional view taken along the line IVa--IVa in FIG. 3;

FIG. 4b is a sectional view taken along the line IVb--IVb in FIG. 3;

FIG. 5 is a bottom view of the discharge element shown in FIG. 3;

FIG. 6 is an enlarged view of a portion D surrounded by the two-dotchain line in FIG. 3;

FIG. 7 is a plan view of the portion shown in FIG. 6 in another state;

FIG. 8 is a plan view of the same portion in still another state;

FIG. 9 is an enlarged sectional view of a linear electrode and a portionnear the electrode in a conventional method of producing a dischargeelement;

FIG. 10 is an enlarged sectional view of the same portion as that shownin FIG. 9 in a production method of the present invention;

FIG. 11 is a longitudinal sectional view of an ion generating apparatusto which the discharge element of the present invention is applied;

FIG. 12 is a plan view of a portion of the apparatus shown in FIG. 11;

FIG. 13a is a sectional view taken along the line XIIIa--XIIIa in FIG.12;

FIG. 13b is a sectional view taken along the like XIIIb--XIIIb in FIG.12;

FIG. 14 is a view of the rear side of the portion shown in FIG. 12;

FIG. 15 is a longitudinal sectional view of another apparatus to whichthe present invention is applied;

FIG. 16 is a line view showing the operating state of the apparatusshown in FIG. 15;

FIG. 17 is a plan view of a conventional discharge element;

FIG. 18a is a sectional view taken along the line XVIIIa--XVIIIa in FIG.17;

FIG. 18b is a sectional view taken along the line XVIIIb--XVIIIb in FIG.17;

FIG. 19 is a view of the rear side of the discharge element shown inFIG. 17;

FIG. 20 is a plan view of another conventional discharge element; and

FIG. 21 is a sectional view taken along the line XXI--XXI in FIG. 20.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show an ozone generating apparatus comprising a dischargeelement of the present invention, and FIGS. 3 to 5 show the dischargeelement as a component of an apparatus.

In FIGS. 3, 4 and 5, a conductor (for example, stainless ceramicconductor or semiconductor) sheet electrode 3 is caused to adhere to therear side of a ceramic insulator sheet (referred to as "sheet"hereinafter) 1, and a ceramic semiconductor linear electrode 2 isprovided in a rectangular form on a portion of the front side of thesheet inwardly of the portion opposite to the sheet electrode 3, aportion of the linear electrode 2 being widened so as to serve as alinear electrode feeding portion 2a. Although an alumina substratehaving good thermal conductivity, purity of 90% or more and a thicknessof 0.2 to 1 mm is generally used as the sheet 1, an aluminum nitride andother ceramic insulator sheets and the like may be used as occasiondemand.

The ceramic semiconductor electrode 2 is formed by a process of flamespray coating, such as plasma spray coating a high-melting point ceramicconductive material such as TiN, TaN or the like so as to generally haveporosity of 2.5 to 12.5% and to adhere the coating to the sheet 1,through a mask corresponding to the shape of the electrode. When adischarge element 4 is used in an ozone generating apparatus, as shownin FIGS. 1 and 2, the element is fixed in an upper space of theapparatus body 5 having an a.c. high voltage source 6 by an elementholding spring 15. In this case, one of the a.c. output terminals of thepower source 6 is welded to the sheet electrode 3 of the dischargeelement 4 through a sheet electrode feeding piece 9 made of a springmaterial having resistance to ozone so as to supply electricity to thesheet electrode 3. The other a.c. output terminal is welded to thelinear electrode feeding portion 2a through a linear electrode feedingpiece 8 made of a spring material having resistance to zone and having acontact portion smaller than the linear electrode feeding portion 2a soas to supply electricity to the linear electrode 2. This structurepermits a silent discharge to be generated over a width of 2 to 10 timesthe thickness of the insulator sheet at both sides of the linearelectrode 2. If air or oxygen is supplied to the front space 13 throughan air inlet 10 of a cover 12 placed on the body 5 gas containing ozonecan be obtained from the outlet 11. In the drawings, reference numeral 7denotes power source input terminals for the a.c. high voltage source 6,which terminals are unnecessary when a battery is used as a powersource. When the discharge element 4 is small, the rear space thereofmay be simply a space, while when the discharge element 4 is large andconsumes much electricity, it is sometimes necessary to provide acooling device for cooling the element on most of the rear side of theelement 4 as illustrated in FIG. 2.

In the case of the ozone generating apparatus shown in FIGS. 1 and 2,since no discharge is generated on the side of the sheet electrode 3 ofthe discharge element 4, the sheet electrode 3 and the feeding piece 8may be made of a ozone-resistant conductive material such as stainlesssteel or the like. However, when it is desired to prevent curvature ofthe sheet electrode 3, the sheet electrode 3 may be formed by plasmaspray coating a ceramic conductive material such as TiN, TaN or the likehaving thermal conductivity which is substantially equal to that of thesheet 1. A projecting portion 5a, on the inside of the body 5 and anotch la of the ceramic insulator sheet 1, of the discharge element 4,form a device for preventing wrong assembly which is provided forpreventing the discharge element 4 from being mistakenly set upside downduring assembly or maintenance service. In the case of the dischargeelement 4 of the present invention, although the sheet electrode 3 issometimes buried in an insulating material, except the feeding portionthereof, as shown in FIGS. 17, 18 and 19, the sheet electrode is notlimited to this. As shown in FIGS. 3, 4 and 5, the sheet electrode 3 mabe exposed to air so that the shortest distance between the linearelectrode 2 and the sheet electrode 3 is sufficiently larger than thecreeping discharge resistant distance of the insulator sheet 1. In thiscase, it is important to round the outer shape of the linear electrode 2and the sheet electrode 3 for obtaining as high a creeping dischargeresistant voltage as possible between the linear electrode 2 and thesheet electrode 3. In another case, a silicone resin is injected intothe rear space 14 shown in FIG. 2 so that the sheet electrode 3 isburied therein. In a further case, as shown in FIGS. 11, 12 and 13, arepellent coating 35 is provided on a portion on the linear electrodeside of the sheet 1 corresponding to the sheet electrode 3 and theportion of the sheet electrode 3 excluding the feeding portion 3a so asto effectively prevent the dielectric breakdown of the discharge element4 from being produced by moisture when air and the like is used as a rawmaterial gas. This is an important feature of the present invention. Inaddition, when air is used as raw material gas for producing ozone,water sometimes adheres to the insulator surface after the operation hasbeen stopped, and thus the apparatus cannot be easily started due to anincrease in electric capacity between the linear electrode 2 and thesheet electrode 3. In order to prevent this phenomenon, the amount ofwater adhering can be decreased by using an alumina substrate (purity,99% or more) having a smooth surface or alumina substrate (purity 95% ormore) in which at least a portion for generating discharge is polished.This is also an important feature of the present invention.

A fundamental important feature of the present invention lies in themethod of producing many discharge elements of high efficiency at lowcost by closely combining the insulator sheet 1 and the semiconductorlinear electrode 2 by flame spray coating, as descrbed above. Theproduction method is described in detail below.

FIGS. 6, 7 and 8 are enlarged views of the portion D near the linearelectrode 2, shown in FIG. 3, of the discharge element of the presentinvention under operation. FIG. 6 shows a case where high efficiency isnot obtained, FIG. 7 shows a case where no substantially satisfactoryefficiency is obtained, and FIG. 8 shows a case where ideal highefficiency is obtained. In FIG. 6, the linear electrode 2 has a shape inwhich projections and recesses are alternately irregularly range at theedge thereof, a strong discharge portion 16 strongly emitting lightbeing produced at each of the projecting portions, and a non-dischargeportion 17 being present in each of the recesses. Thus, the ozoneproduced in the strong discharge portions 16 is decomposed due to thehigh temperature thereof, and no ozone is generated in the recesses,thereby decreasing the overall efficiency of generation of ozone. As aresult, a sufficiently high efficiency cannot be exhibited. The cause ofthis phenomenon is explained by the enlarged sectional view taken alongthe line vertical to the linear electrode during production in FIG. 9.In FIG. 9, the linear electrode material which is melted by flame spraycoating scatters and enters a portion under the masking metal plate 19-bwhere the masking metal plate 19-b insufficiently adhere to the sheet 1to form a projecting portion 2-19-b in the linear electrode. Conversely,a recess 2-19-a is formed in the linear electrode 2-19 in a portionwhere the masking metal plate 19-a sufficiently adheres to the sheet 1.As a result, projections and recesses irregularly range at the edge ofthe linear electrode 2, as shown in FIG. 6. Since, in such a phenomenon,the projections and recesses at the edge of the electrode are of amicron size, they cannot be effectively removed in many cases byemploying a method of causing the masking metal plate made of a magneticmaterial to adhere to the sheet 1 using a strong magnet on the rear sidethereof. FIG. 10 shows the feature of the method of producing ahigh-efficiency discharge element in accordance with the presentinvention which is capable of solving the problem. FIG. 10 is anenlarged sectional view taken along the line vertical to the linearelectrode during the production of the electrode. In FIG. 10, a maskingmember 20 mainly composed of a heat-resistant resin is formed on thesheet 1 by screen printing so as to adhere thereto and, if required, canbe subjected to a dry-baking process. A linear electrode 2-20 is thenformed by flame spray coating. This method prevents the linear electrodematerial from entering under the masking member 20 and thus enables theformation of the linear electrode having no irregularity at the edgethereof, as shown in FIG. 8. It is therefore possible to generateuniform discharge 18 during operation and obtain high efficiency of thegeneration of ozone. The above-described feature that uniform dischargeis generated near the linear electrode is a very important feature of ageneral discharge element comprising a sheet electrode and a linearelectrode with a ceramic insulator sheet therebetween and used forgenerating ozone or extracting ions.

After the linear electrode has been produced, the masking member 20 canbe removed by sandblasting or scraping by a wire brush. Although thematerial for the masking member 20 depends upon the material requiredfor the electrode and production speed thereof, the masking member 20 ispreferably mainly made of a resin material having resistance to heat at150° C. or more and adhesion to the sheet 1 which is not excessivelyhigh. Examples of such materials include epoxy-modified polyparabanicacid, silicone resins, fluorine resins and the like. In the productionmethod characterized by adhesion of the masking member 20 to the sheet1, the removal of the masking member 20 after the linear electrode isformed is also an important process, and the above-described dry processis preferred. From this viewpoint, the masking member 20 preferably hasadhesion to the sheet 1 which is not excessively high. Although ageneral resist agent used for processing printed substrates can be usedas the masking member 20 so that the electrode can be formed by flamespray coating after the electrode portion of the masking member has beenremoved by photosensitive treatment, the method often costs much. Anaqueous material can be used as a main component of the masking member,and, in some cases, the material can be used in an uncured form. In thiscase, since the masking member can be removed simply by water washing,the cost is sometimes reduced. In order to prevent a decrease in theefficiency of the element which is caused by the nonuniform dischargeproduced due to the projections formed at the edge shown in FIG. 6, thedischarge state shown in FIG. 6 can be improved to the state having thedischarge portion 16a and the non-discharge portion 17 shown in FIG. 7or the state having the uniform discharge portion 18 shown in FIG. 8 byapplying to the element a voltage of 1 to 1.5 times a usual appliedvoltage for aging the element for about 1 to 10 hours. When an apparatuscomprising the discharge element in accordance with the presentinvention is used for processing a semiconductor, the material for thelinear electrode of the element is preferably a high-melting pointceramic conductive material such as TiN, TaN or the like. When theapparatus is used for other purposes, borides and carbides of thetransition metals in Groups IVa, Va in the Periodic Table can be used.

FIG. 11 shows a basic arrangement of the present invention concerning asystem for utilizing the discharge element in an ion generatingapparatus, a charging apparatus, a destaticizing apparatus or the like.

In FIG. 11, an a.c. silent creeping discharge having a certain relationto the frequency of the a.c. power source 6 is generated on the surfaceof the discharge element on the linear electrode side, and plasmacontaining positive and negative ions and electrons is periodicallygenerated. For example, if a potential setting power source 36 isinterposed between the discharge element and the earth, and if anearthed counter electrode 31 is provided opposite to the dischargeelement, an electrical field is generated between the discharge elementand the counter electrode depending upon the polarity and voltage of thepotential setting power source 36 so that ions with a specified polarityare extracted from the plasma and fly through the space 37 toward thecounter electrode 31. For example, if a negative d.c. power source isused as the potential setting power source 36, negative ions areextracted from the discharge element, while if a positive power sourceis used, positive ions are extracted. If an a.c.power source is used,positive and negative ions are alternately extracted toward the space37. In this case, the frequency of the power source 36 must be lowerthan that of the power source 6, as a general rule. In this way, the iongenerating apparatus in accordance with the present invention shown inFIG. 11 allows the amount of ions generated to be adjusted over a widerange by controlling the power source 6. The ion generating apparatusalso has the remarkable characteristic that the field strength of thespace where ions are present and the polarity of ions can be freelyselected independently of the amount of ions generated. Thecharacteristics described in detail above with reference to FIGS. 1 to14 enable the apparatus to secure a long life and a wide operating rangewhen being put into practical use. The ion generating apparatus shown inFIG. 11 can be used as a charging apparatus when a d.c. power sourcehaving a desired polarity is used as the potential setting power source36, and when powder or granules are passed through the space 37 at ahigh speed as shown by arrows 33, 34 in FIG. 11, so that the power orgranules can be charged with a desired polarity. Similarly, when an a.c.power source is used as the potential setting power source 36, and whenan article is passed through as shown by the arrows 33, 34 so that thearticle can be exposed to many negative and positive ions, the apparatuscan be used as a high-efficiency destaticizing apparatus. In addition,when a solid or liquid particles are slowly passed through space 37, thefunctions of both the charge and the Coulomb's force enable theapparatus to be used as a high-efficiency electrical dust-collectingapparatus or an electrostatic coating apparatus. In this case, referencenumeral 31 denotes a dust-collecting electrode or an article to becoated, and reference numeral 32 denotes collected dust or a coatedlayer. Further, when the counter electrode 31 serves as a conductivebase for an electronic copying machine, and when reference numeral 32denotes a high-resistance photosemiconductor layer formed on the counterelectrode 31, the apparatus can be used as an apparatus for charging asemiconductor layer, a transfer charging apparatus or a destaticizingapparatus. In this case, the present invention has marked advantageswith respect to speeding up of an electronic copying machine, softeningof gradation, increasing the service cycle period and the like. Theshape of the conductive base of an electronic copying machine is notlimited to a plane, and a cylindrical shape and other shapes can be usedas occasion demands. When the ion generating apparatus of the presentinvention is applied to a charging apparatus where fine particles arepresent, the ion generating apparatus has the significant characteristicthat the particle repulsing effect of the nonuniform electrical fieldformed between the linear electrode 2 and the sheet electrode 3fundamentally prevents the particles from collecting and adhering to theelectrodes. This effect is a significant feature of the presentinvention shown in FIGS. 1 to 14.

FIG. 15 shows an apparatus according to an embodiment of the presentinvention in which an article can be electrically charged ordestaticized symmetrically from both sides thereof. In FIG. 15, if powersources 6A, 36A, 6B, 36B are operated with the time relation shown byFIG. 16, ions are extracted from an electrode 2A in the direction of aarrow 47a in a half cycle 47, and ions are extracted from an electrode2B in the direction of a arrow 48a in a half cycle 48. The ionsextracted in all half cycles have a positive polarity so that thearticle passed through space 37 in the direction of arrows 33, 34 can becharged with ions with the same polarity from both sides. In addition,since the average potential of both elements is constantly zero, thearticle is not attracted to one of the elements by the Coulomb's force,particularly high efficiency is exhibited when a high-resistance articleis charged When it is desired to obtain a negative charge, the relativerelation between power sources 36A, 6A and 36B, 6B may be shifted by ahalf cycle. Since positive and negative ions are alternately extractedfrom both discharge elements in each half cycle, the apparatus can beused as a strong destaticizing apparatus.

As described above, the present invention comprises a ceramic insulatorsheet and a high-melting point semiconductor linear electrode, havingrelatively low electric resistance, provided on the sheet so as toadhere thereto. When discharge is produced from the linear electrodesurface toward the sheet electrode, the linear electrode is slightlyworn due to the great heat generated by ion corrosion, even though thetemperature in the linear electrode is increased because the electrodeis made of a high-melting point ceramic semiconductor. In addition,since the linear electrode is not melted and does not scatter and adhereto the surface of the ceramic insulator, no disturbance occurs in thedischarge, and uniform discharge is thus generated over the wholesurface. It is therefore possible to generate sufficient discharge at arelatively low voltage and easily handle the discharge element with asimple structure.

Further, since the linear electrode is produced by flame spray coatingthrough a masking formed by screen printing and adhering to the sheetand, if required, subjected to aging, the linear electrode has noirregularity, and extremely uniform creeping discharge is performed byan a.c. high voltage. When the discharge element is used in an ozonegenerating apparatus, therefore, highly efficient ozone generator isobtained. When the element is used in a charging apparatus, a chargingeffect with good uniformity can be obtained. In addition, the maskingmember can be easily removed from the electrode, and many elements canbe produced at low cost in a short time.

Since a silent discharge generating apparatus in accordance with thepresent invention has an electrode portion, which is made of anozone-resistant material generating no discharge in some operatingstates, connected to a feeding piece made of an ozone-resistantmaterial, it is easy to produce, maintenance and assembly the elementand apparatus.

What is claimed is:
 1. A discharge element, comprising:a sheetelectrode; a semiconductor electrode, said electrode formed from amaterial selected from the group consisting of TiN and TaN, saidsemiconductor electrode having at least a straight portion, wherein saidsemiconductor electrode has a porosity of 2.5 to 12.5% whereby saidsemiconductor electrode has side edges of sufficient smoothness togenerate even discharge over the full length of said side edges; and aceramic dielectric substrate positioned between said sheet electrode andsaid semiconductor electrode, wherein said semiconductor electrode andsaid sheet electrode are attached to opposite surfaces of saidsubstrate.
 2. A discharge element according to claim 1, wherein saidsemiconductor electrode is formed by plasma spray coating.
 3. Adischarge element according to claim 1, wherein said semiconductorelectrode further includes a feeding portion with resistance to ozone.4. A discharge element according to claim 2, further including a feedingportion of said sheet electrode having resistance to ozone.
 5. Adischarge element according to claim 1, wherein a portion of saidceramic dielectric substrate is coated with an insulator havingresistance to ozone.
 6. A discharge element according to claim 1,wherein a portion of said ceramic dielectric substrate is coated with anozone-resistant insulating material having water repellency.
 7. A silentdischarge generating apparatus comprising:a discharge element having asheet electrode and a semiconductor electrode, said semiconductorelectrode formed by plasma spray coating such that said semiconductorelectrode has a porosity of 2.5 to 12.5%, said semiconductor electrodehaving at least a straight portion and including smooth side edges,whereby said semiconductor electrode is durable and generates an evendischarge along the entire length of said side edges; and a ceramicinsulator sheet between said sheet electrode and said semiconductorelectrode so that a silent discharge is generated around saidsemiconductor electrode when a voltage from an a.c. voltage source isapplied between said sheet electrode and said semiconductor electrode.8. A silent discharge generating apparatus according to claim 7, whereinsaid discharge element is resistant to ozone.
 9. A silent dischargegenerating apparatus according to claim 7 further including a feedingpiece for applying a voltage to said discharge element from said a.c.voltage source, said feeding piece being made of a conductive materialhaving resistance to ozone.
 10. A silent discharge generating apparatusaccording to claim 9, wherein said feeding piece contacts the feedingportions of both said electrodes.
 11. A silent discharge generatingapparatus according to claim 7, further comprising a cooling devicecarried on said sheet electrode.
 12. A silent discharge generatingapparatus according to claim 7, wherein said discharge element isresistant to ozone.
 13. A silent discharge generating apparatusaccording to claim 7, wherein said discharge element is resistant toozone and has water repellency.
 14. A silent discharge generatingapparatus comprising:a first sheet electrode; a second electrode formedfrom a material selected from the group consisting of TaN and TiN,second said electrode having a porosity of 2.5 to 12.5% whereby sideedges of said second electrode are smooth such that said secondelectrode generates an even discharge over the full length of said sideedges; and a ceramic insulator sheet between said first sheet electrodeand said second electrode, wherein a voltage is applied between saidfirst sheet electrode and said second electrode to generate a uniformsilent discharge around said second electrode.
 15. A discharge elementcomprising a sheet electrode and a semiconductor electrode includingsmooth side edges, said semiconductor electrode including at least astraight first portion and a feeding portion, said semiconductorelectrode formed by plasma spray coating a material selected from thegroup consisting of TiN and TaN on an insulator sheet, saidsemiconductor electrode having a porosity of 2.5 to 12.5%, and saidfirst portion having an ozone resistant insulating coating.
 16. Adischarge element as described in claim 15 wherein said first portion ofsaid semiconductor electrode has water repellency.
 17. A dischargeelement comprising:a ceramic insulator sheet; a semiconductor electrodeformed on one surface of said ceramic insulator sheet, saidsemiconductor electrode having at least a straight portion; and a sheetelectrode formed on another surface of said ceramic insulator sheet,wherein said semiconductor electrode is formed from a material selectedfrom a group consisting of TiN and TaN and has a porosity of 2.5 to12.5% whereby side edges of said semiconductor electrode are smooth suchthat they generate an even silent discharge over the full length of saidside edges when an AC power source is connected between said electrodes.